1. Field of the Invention
The present invention relates to a lens device and more particularly, to the structure of an operating member used to move a moving lens in the optical axis direction.
2. Description of the Related Art
In recent years, monitoring cameras have been installed in, for example, financial institutions or stores where merchandise is offered for sale. The monitoring camera is attached to the ceiling or wall of an installation site, such as an entrance or an elevator. After the monitoring camera is installed at a predetermined position, for example, a zoom lens or a focus lens is adjusted according to the installation environment.
JP-A-2007-310228 (corresponding to US-A-2007/0268596) discloses a monitoring camera in which an operation ring for focusing and an operation ring for zooming are provided on the object side of the camera and the focusing and zooming operations are performed after the camera is installed. In this way, the operability of the monitoring camera is improved.
With an improvement in the performance of image sensors applied to the monitoring cameras (with an increase in the number of pixels), the purpose of the monitoring camera has been changed from the recording of images to the recognition of the details of images. When the number of pixels of the image sensor increases, a delicate operation is required for zooming or focusing. As a result, it is difficult to perform the zooming or focusing operation and it takes a long time to perform the zooming or focusing operation.
Here, an example of the structure according to the related art that moves a moving lens, such as a zoom lens or a focus lens, will be described. FIG. 7 is a plane development diagram schematically illustrating the structure of a lens barrel 200 (a moving lens is supported so as to be movable in the optical axis direction and an operating member used to move the moving lens is attached to the lens barrel) according to the related art.
FIG. 7 shows a lens supporting portion of the lens barrel and an attachment portion of the operating member. As shown in FIG. 7, three straight-ahead grooves 204A, 204B, and 204C are provided in the outer circumferential surface 202 of the lens barrel (fixed cylinder) 200 in parallel to the optical axis direction. The three straight-ahead grooves 204A, 204B, and 204C are arranged at equal intervals of 120° in the circumferential direction of the fixed cylinder 200. Three pins 206A, 206B, and 206C that are arranged at equal intervals of 120° on the outer circumferential portion of a lens frame (not shown) to which the moving lens is fixed are fitted to the three straight-ahead grooves 204A, 204B, and 204C. The three pins 206A, 206B, and 206C are also fitted to spiral cam grooves 208A, 208B, and 208C (represented by a one-dot chain line in FIG. 7) that are provided in the inner circumferential surface of the operating member (a rotating cylinder attached to the outer circumferential surface of the fixed cylinder 200; not shown).
In the lens device having the above-mentioned structure, when the rotating cylinder is rotated with respect to the fixed cylinder 200 to move the cam grooves 208A, 208B, and 208C in the vertical direction of FIG. 7, the pins 206A, 206B, and 206C are moved along the intersections of the straight-ahead grooves 204A, 204B, and 204C and the cam grooves 208A, 208B, and 208C, respectively. In this way, it is possible to move the moving lens forward or backward in parallel to the optical axis direction, which is the left-right direction of FIG. 7.
As a structure for regulating the movement range of the rotating cylinder, an opening 210 with a predetermined length is provided in the outer circumferential surface of the rotating cylinder along the circumferential direction, and a rotation regulating pin 212 is inserted into the groove provided in the outer circumferential surface of the fixed cylinder 200 through the opening 210. The amount of rotation of the rotating cylinder is regulated by the length of the opening 210 in the circumferential direction, and the rotation regulating pin 212 is fitted to the fixed cylinder 200 to fix the relative position (lens position) between the fixed cylinder 200 and the rotating cylinder.
Guide grooves 214A, 214B, and 214C are provided in the outer circumferential surface 202 of the fixed cylinder 200 at equal intervals of 120° in the circumferential direction so as to correspond to the straight-ahead grooves 204A, 204B, and 204C. The guide grooves 214A, 214B, and 214C regulate the movement of the rotating cylinder in the axial direction when the rotating cylinder is fitted to the fixed cylinder 200 and are used to determine the positions of the rotating cylinder and the fixed cylinder 200 when the rotating cylinder is fitted to the fixed cylinder 200. Pins (claw portions hatched in FIG. 7) 216A, 216B, and 216C that are provided on the inner circumferential surface of the rotating cylinder are fitted to the guide grooves 214A, 214B, and 214C to determine the positions of the rotating cylinder and the fixed cylinder 200 when the rotating cylinder is fitted to the fixed cylinder 200.
However, in the adjustment structure of the moving lens shown in FIG. 7, it is difficult to widen the movement range of the rotating cylinder to be equal to or more than the length of the guide grooves 214A, 214B, and 214C of the fixed cylinder 200 in the circumferential direction. The movement range of the rotating cylinder is determined by the fitting of the rotation regulating pin 212 to the opening 210, not the fitting of the pins 216A, 216B, and 216C to the guide grooves 214A, 214B, and 214C. Therefore, it is necessary to provide a clearance between both ends of each of the guide grooves 214A, 214B, and 214C such that the pins 216A, 216B, and 216C do not collide with the guide grooves 214A, 214B, and 214C.
For example, in the case of the guide groove 214B, the movement range of the rotating cylinder is from the position of the pin 216B to the position of a pin 216B′, and the limit of the angle of the movement range is equal to or less than 100°. In fact, the limit of the angle is in the range of 60° to 80°.
As such, the amount of operation of the rotating cylinder needs to be very small in order to finely move the moving lens under the conditions where the movement range of the rotating cylinder is regulated. As a result, it is very difficult to perform a zooming or focusing operation. When the size of the lens device is reduced, it is more difficult to perform the zooming or focusing operation of finely moving the moving lens. In order to change the movement range of the moving lens, the overall design of the lens needs to be reexamined. Therefore, it is difficult to change the movement range of the moving lens. Thus, it is preferable to facilitate the zooming or focusing operation without changing the movement range of the moving lens. In this case, even though the movement range of the rotating cylinder is wide and the amount of operation of the rotating cylinder is large, a structure with a small amount of lens movement may facilitate the zooming or focusing operation.